Title : A novel subsurface description for jurassic marrat formation for improved reservoir management in greater Burgan Field, Kuwait
Abstract:
Introduction
A new depositional and stratigraphic framework is proposed for Middle Marrat reservoirs. They are designed to improve the reservoir management and development plan in the Greater Burgan Field.
The Middle Marrat reservoir of Kuwait was deposited during the Lower Jurassic Pliensbachian to Toarcian period, approximately 175-185 Ma, in a low-angle carbonate ramp setting on the neo-Tethys passive margin (Sharland et al., 2001). It comprises stacked shallow marine grainstone shoals and finer grained lagoonal and ramp sediments. The depositional architecture is overprinted by a range of diagenetic processes both reducing and enhancing reservoir quality.
The Greater Burgan Field has three different structural culminations i.e. Burgan, Magwa and Ahmadi. (Figure 1). Exploration and development activities in Middle Marrat of Greater Burgan Field is continuing since early 1980s.Drilling and production in Magwa field continued from that time, whereas Burgan exploration was halted intermittently and was finally development activities started from 2018. Ahmadi culmination was found to be unproductive. So far more than 80 wells have been drilled in Marrat Formation of Greater Burgan Field.
With continuing development of both Magwa and Burgan structures in Greater Burgan Field, a need for revision of the existing depositional and stratigraphic framework was felt to support reservoir management, infill drilling and future water injections.
Method and/or Theory
Depositional Model:
Twenty-two Middle Marrat cores (~5500ft of core) were interpreted during this study and used to develop a thorough understanding of depositional facies, facies associations and depositional environments).
These data were integrated with available petrography, well logs, dynamic, and seismic data and used to develop a facies scheme and depositional models. Two depositional models have been developed, both of which are consistent with core data and the limited biostratigraphic data which confirm a shallow water carbonate ramp setting.
- “Ramp Barrier Model” which implies that the Middle Marrat member over Greater Burgan formed a barrier which created a land-attached subtidal lagoon behind it which progressively passes onto tidal flats and sabkha environments towards West Kuwait. This model, in the context of a very low angle carbonate ramp, would have resulted in relatively large-scale low-energy facies belts and relatively narrow and disconnected shoal belts.
- “Ramp Bank Model” which predicts one or more isolated banks or islands in an otherwise mid-ramp setting, with each island forming on a relative bathymetric high, formed by local depositional or structural effects, or possibly a combination of the two.
It is important to stress out that both models are thought to be valid for the Middle Marrat member and most likely occurred in various proportions at different times and over different areas of Kuwait, with the ramp barrier model seen as dominant, based on the regional correlation work and the ramp bank model seen as more localized and episodic.
